1. Field of the Invention
This invention relates to a packaging technique for pressure transducers and, more specifically, to such packaging for pressure transducers capable of measuring high pressures in the range of up to about 5000 psi.
2. Brief Description of the Prior Art
Pressure sensors containing pressure transducers are well known, typical such systems being described in U.S Pat. Nos. 4,726,492 and 4,774,626.
Pressure transducers of the prior art have generally been fabricated by providing a pressure sensing module including an electronic circuit having a variable capacitor responsive to fluid pressure. The electronic circuit sensed the capacitance of the capacitor and provided an output through a plastic electrical connector indicative of the sensed pressure. The transducer elements were arranged such that a metal cup assembly having an opening or fluid pressure inlet at one end thereof to receive the fluid under pressure to be measured also included therein the pressure sensing module. The pressure sensing module was spaced from the inlet by a gasket or O-ring, the electronic circuit and connector also being contained within the metal cup. The parts were held together within the metal cup by crimping the metal cup over the plastic connector, the latter being used as a support member.
The above described pressure transducer provided highly satisfactory results when operated in the low to moderate pressure ranges of up to 500 to 600 psi. However, when subjected to pressures at the pressure inlet in the range of about 3000 to 5000 psi and up, the above described pressure transducers tended to fail. There were several points of failure, these being mainly from the inability of the plastic connector to support the high pressures to which it was being subjected. More specifically, the crimp at the metal cup was unable to retain the electrical connector crimped thereunder with the result that the connector was moved out of the cup and caused a failure of the transducer. A further point of failure was the plastic connector itself which tended to shear or compress and release the gasket or O-ring under the high pressure and release the fluid under pressure from the interior of the pressure transducer. It is therefore clear that the prior art pressure transducer of the type described hereinabove was incapable of reliable operation in a high pressure environment.
The above described problem of the prior art was materially improved in accordance with the the packaging techniques described in the above mentioned Ser. No. 07/282,185, filed Dec. 8, 1988 wherein the pressure sensing element is isolated from the connector by being disposed in an all metal surrounded cavity whereby the plastic connector is separated from the pressure transducer element and is not bearing the loads produced by the high pressure fluid. This is accomplished by a metal member disposed between the pressure sensing element and the plastic connector whereby the high pressures encountered by the pressure transducer are never applied to the plastic connector. However, though the pressure transducers of this application provide highly satisfactory results, there remains the problem that the internal pressures within the transducer are equal to the applied high pressure to be measured. This places all structural members of the package as well as the seal mechanism in a highly stressed state. It is therefore apparent that any diminution of the stresses applied within the package will result in improved transducer life and will materially relieve those problems caused by such internal stresses which have previously been minimized by costly design measures.